1. Field of the Invention
The present invention relates to a tiltable vehicle steering mechanism, and more particularly to an electrically operated tiltable vehicle steering mechanism. More specifically, the present invention pertains to a vehicle steering mechanism wherein a rotation of an electric motor is converted into a linear motion by means of a screw-nut mechanism, the linear motion being transferred through a linkage to a tiltable bracket which supports a steering shaft to thereby produce a tilting motion of the tiltable bracket and the steering shaft.
2. Description of the Prior Art
An example of an electrically operated tiltable vehicle steering mechanism is disclosed by the Japanese patent Application (Publication) No. 59-230861 in which a stopper device is provided in the screw-nut mechanism to limit the stroke of the screw shaft. According to the proposal by the Japanese patent application, the screw-nut mechanism includes a nut engaged with a screw shaft so that the nut is moved in the axial direction upon a rotation of the screw shaft. The nut is provided at the opposite axial ends with stopper shoes which are adapted to be brought into abutting engagement with stopper plates provided on the housing of the screw-nut mechanism.
In the proposed mechanism, the stopper shoes are formed by rubber or similar resilient material which are of relatively large frictional coefficient so that the shoes do not slip or slidably move with respect to the stopper plate when the shoes are brought into abutting engagement with the stopper plates. It should however be pointed out that such slipless engagement between the stopper shoes and the stopper plate is disadvantageous in view of the life of the stopper device, because the nut is applied with a certain amount of rotative force by the screw shaft and the stopper shoes are deformed not only in the axial direction but also in the circumferential direction when they engage the stopper plates.
Further, in said Japanese patent disclosure the screw-nut mechanism will be subjected to damage when the steering shaft is moved to an extreme position over its predetermined stroke or an excessive load is applied to the steering shaft.